Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
  • H01S5/00—Semiconductor lasers
  • H01S5/02—Structural details or components not essential to laser action
  • H01S5/026—Monolithically integrated components, e.g. waveguides, monitoring photo-detectors, drivers
• • G—PHYSICS
  • G02—OPTICS
  • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
  • G02F2/00—Demodulating light; Transferring the modulation of modulated light; Frequency-changing of light
  • G02F2/004—Transferring the modulation of modulated light, i.e. transferring the information from one optical carrier of a first wavelength to a second optical carrier of a second wavelength, e.g. all-optical wavelength converter
• • G—PHYSICS
  • G02—OPTICS
  • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
  • G02F2/00—Demodulating light; Transferring the modulation of modulated light; Frequency-changing of light
  • G02F2/004—Transferring the modulation of modulated light, i.e. transferring the information from one optical carrier of a first wavelength to a second optical carrier of a second wavelength, e.g. all-optical wavelength converter
  • G02F2/006—All-optical wavelength conversion
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
  • H01S5/00—Semiconductor lasers
  • H01S5/005—Optical components external to the laser cavity, specially adapted therefor, e.g. for homogenisation or merging of the beams or for manipulating laser pulses, e.g. pulse shaping
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
  • H01S5/00—Semiconductor lasers
  • H01S5/02—Structural details or components not essential to laser action
  • H01S5/022—Mountings; Housings
  • H01S5/023—Mount members, e.g. sub-mount members
  • H01S5/02325—Mechanically integrated components on mount members or optical micro-benches
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
  • H01S5/00—Semiconductor lasers
  • H01S5/06—Arrangements for controlling the laser output parameters, e.g. by operating on the active medium
  • H01S5/062—Arrangements for controlling the laser output parameters, e.g. by operating on the active medium by varying the potential of the electrodes
  • H01S5/0625—Arrangements for controlling the laser output parameters, e.g. by operating on the active medium by varying the potential of the electrodes in multi-section lasers
  • H01S5/06255—Controlling the frequency of the radiation
  • H01S5/06256—Controlling the frequency of the radiation with DBR-structure
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
  • H01S5/00—Semiconductor lasers
  • H01S5/20—Structure or shape of the semiconductor body to guide the optical wave ; Confining structures perpendicular to the optical axis, e.g. index or gain guiding, stripe geometry, broad area lasers, gain tailoring, transverse or lateral reflectors, special cladding structures, MQW barrier reflection layers
  • H01S5/22—Structure or shape of the semiconductor body to guide the optical wave ; Confining structures perpendicular to the optical axis, e.g. index or gain guiding, stripe geometry, broad area lasers, gain tailoring, transverse or lateral reflectors, special cladding structures, MQW barrier reflection layers having a ridge or stripe structure
  • H01S5/227—Buried mesa structure ; Striped active layer
  • H01S5/2275—Buried mesa structure ; Striped active layer mesa created by etching
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
  • H01S5/00—Semiconductor lasers
  • H01S5/50—Amplifier structures not provided for in groups H01S5/02 - H01S5/30
  • H01S5/5009—Amplifier structures not provided for in groups H01S5/02 - H01S5/30 the arrangement being polarisation-insensitive
  • H01S5/5018—Amplifier structures not provided for in groups H01S5/02 - H01S5/30 the arrangement being polarisation-insensitive using two or more amplifiers or multiple passes through the same amplifier
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
  • H01S5/00—Semiconductor lasers
  • H01S5/50—Amplifier structures not provided for in groups H01S5/02 - H01S5/30
  • H01S5/5054—Amplifier structures not provided for in groups H01S5/02 - H01S5/30 in which the wavelength is transformed by non-linear properties of the active medium, e.g. four wave mixing

Definitions

• the invention relates to a method and apparatus for integrated wavelength tunable single and two-stage all-optical wavelength converter.
• WDM wavelength-division multiplexing
• packet switching network architectures are essential components for a wide variety of wavelength-division multiplexing (WDM) and packet switching network architectures. They can be used as replacement sources in long haul dense WDM communication systems or for wavelength routing in access networks. They are also important devices for next generation phased array radar systems that use true-time delay beam steering. There is a need in such systems for stable monolithic integrated optical frequency converters, but until now none have been available.
• the invention is an apparatus comprising a semiconductor heterostructure, a tunable laser fabricated in the semiconductor heterostructure and an interferometer having an input coupled to the output of the tunable laser.
• the interferometer is monolithically fabricated with the tunable laser in the semiconductor heterostructure.
• the tunable laser is a distributed Bragg reflector laser, although the invention contemplates any type of semiconductor laser now known or later devised.
• the laser also comprises a buried ridge stripe waveguide laser.
• the buried ridge stripe waveguide laser comprises two sampled grating DBR mirrors, a gain section and a phase section.
• the interferometer has a semiconductor optical amplifier coupled in each its arms.
• the apparatus further comprises a cross-gain semiconductor optical amplifier converter coupled to the interferometer.
• the semiconductor optical amplifier coupled in each arm is biased so that an optical path length 25 difference between the two arms is in antiphase which results in destructive interference.
• the semiconductor optical amplifier is polarization insensitive.
• the apparatus has an input to which an input signal, ⁇ i, is coupled and a coupler.
• the polarization insensitive semiconductor optical amplifier has an output coupled to the coupler.
• the output of the tunable laser is coupled to the coupler.
• the polarization insensitive semiconductor optical amplifier is used as a gain controller for the semiconductor optical amplifiers in the interferometer to allow wavelength conversion over a larger range of input signal powers.
• a dense wavelength division multiplexing communication system with multiple channels is coupled to the output of the interferometer so that the tunable laser can be used to convert between any two of the multiple channels.
• the interferometer further comprises a multimode interference coupler characterized by a wavelength insensitive splitting ratio coupled to the input of the interferometer.
• the heterostructure substrate comprises a low bandgap waveguide layer and thinner multi-quantum well active regions disposed above the low bandgap waveguide layer.
• the heterostructure substrate has nonabsorbing passive elements formed therein by selectively removing the quantum wells regions above the waveguide layer to allow formation of active and passive sections in the waveguide layer without having to perform a butt joint regrowth.
• an input signal, ⁇ i is coupled thereto and the apparatus further comprises a distributed feedback laser having an output to 25 modulate the input signal, ⁇ i.
• a semiconductor optical amplifier has an output and an input coupled to the input signal, ⁇ ; and to the output of the distributed feedback laser.
• a notch filter has an output and an input coupled to the output of the semiconductor optical amplifier.
• An input of the interferometer is coupled to the output of the notch filter, so that the input signal, ⁇ is converted to a desired wavelength via cross phase modulation.
• a comb filter has its input coupled to the output of the interferometer.
• the semiconductor optical amplifier has an input coupled to the input signal, ⁇ and is polarization insensitive. The interferometer is operated at a fixed polarization of an intermediate wavelength.
• the apparatus further comprises a distributed feedback laser having an output to modulate the input signal, ⁇ i..
• a semiconductor optical amplifier has an input coupled to the input signal, ⁇ i, and to the output of the distributed feedback laser.
• a notch filter has an input coupled to the output of the semiconductor optical amplifier.
• the input of the interferometer is coupled to the output of the notch filter, so that the input signal, ⁇ j , is converted to a desired wavelength via counter propagating cross gain modulation.
• a comb filter has an input coupled to the output of the interferometer.
• the invention is also characterized as a method of fabricating an integrated optical device comprising providing a base structure comprised in turn of a cap layer, a multiquantum well layer disposed beneath the cap layer, a first waveguide layer disposed beneath the multiquantum well layer, and a heterostructure waveguide layer disposed beneath the first waveguide layer.
• the cap layer and multiquantum well layer are selectively removed to define a passive section.
• An MOCVD layer is regrown on the passive section and the 25 remaining portions of the base structure.
• Optical structures are then selectively formed in the MOCVD layer, the passive section and remaining portions of the base structure.
• the step of selectively forming optical structures in the MOCVD layer, the passive section and remaining portions of the base structure comprises forming an active optical device in the remaining portions of the base structure, or more particularly a laser or an optical grating.
• the step of selectively forming optical structures in the MOCVD layer, the passive section and remaining portions of the base structure also comprises forming a passive optical device in the passive section, such as a spot size converter.
• the step of selectively forming optical structures in the MOCVD layer, the passive section and remaining portions of the base structure comprises forming a tunable laser and at least two semiconductor optical amplifiers in the remaining portions of the base structure, an interferometer in the passive section and a waveguide circuit coupling the laser, at least two semiconductor optical amplifiers, and interferometer into an optical circuit to form an at least partially integrated tunable wavelength converter.
• Fig. 1 is a diagrammatic perspective view of a photonic chip in which a single stage wavelength converter has been fabricated.
• Fig. 2 is a block diagram of the elements of a photonic two stage wavelength converter in which non-integrated components are used.
• Fig. 3 is a diagrammatic perspective view of a photonic chip in which a two stage wavelength converter has been fabricated in an integrated manner.
• Figs. 4a - 4i(4) are simplified cross-sectional diagrams, which illustrate the method by which the optical devices of the invention are fabricated in an integrated fashion.
• This invention is a device and method for performing an all optical wavelength conversion using a tunable laser 10 integrated with single stage and two-stage Mach-Zehnder interferometer converter configurations 12 and 14 respectively best depicted in Figs. 1 and 3.
• One aspect of this implementation is integration of a widely tunable sampled grating distributed Bragg reflector (DBR) laser 10 that can be vernier tuned over more than 40 nm and is optically isolated from the wavelength converter sections 12 and 14 due to the DBR mirror section in laser 10. This isolation overcomes fundamental limitations of previous attempts to integrate these devices. See also copending U.S. Patent Application serial no. , entitled “Tunable Laser Source with Integrated Optical Modulator,” claiming priority to Provisional Patent Application serial no. 60/152,432 filed on Sept. 2, 1999, which are both incorporated herein by reference.
• DBR distributed Bragg reflector
• the single-stage wavelength converter 12 in Fig. 1 comprises a Mach- Zehnder interferometer 12 combined with semiconductor optical amplifiers (SO As) 16 and 18 in each arm 20 and 22 of interferometer 12.
• the two-stage converter 14 in Fig. 3 is comprised of a cross-gain semiconductor optical amplifier converter followed by the Mach-Zehnder interferometer based converter 16, 18, 20, 22.
• the input signal ⁇ i is amplified by semiconductor optical amplifier 38, combined with the output of tunable laser 10 in a coupler 40 and fed to semiconductor optical amplifier 18 in arm 22 of interferometer 12.
• the optical power fed into semiconductor optical amplifier 18 modifies the transfer function through amplifier 18 resulting in an amplified output signal at ⁇ i and ⁇ m .
• ⁇ i can then be filtered out by a conventional off-chip optical filter (not shown).
• Semiconductor optical amplifier 16 is provided in the opposing arm 20 ol interferometer 12 to adjust optical path lengths between arms 20 and 22. Amplifiers 16 and 18 can be biased so that the optical path length difference 25 between the two arms 20 and 22 is in antiphase resulting in destructive interference at the output waveguide 24.
• the input signal, ⁇ j is coupled into a single arm 22 of the interferometer 12, 14. When the input light, ⁇ j, is in the high power state, it changes the phase difference between the two arms 20 and 22 and allows light from the pumped beam, ⁇ m , to be transmitted.
• This method transfers the modulation on the input data signal, ⁇ ;, to the pumped light, ⁇ m , from the tunable laser 10 which can be performed with or without logical bit inversion by selectively operating on the appropriate slope of the transfer curve of semiconductor optical amplifier 18.
• the input beam, ⁇ j can be filtered out at the output 24 allowing the converted light to be transmitted.
• a monolithic tunable wavelength converter 11 has advantages over an implementation based upon discrete components in that it eliminates two fiber pigtails that increase the noise figure due to additional insertion loss and packaging expense.
• the tunable nature of this implementation also allows one device to be used to optically convert between any two channels in a dense wavelength division multiplexing (DWDM) communication system as opposed to a separate untunable device for each channel.
• DWDM dense wavelength division multiplexing
• a feature of the implementation of Figs. 2 and 3 is the use of an internal wavelength between stages to avoid the need for fast tunable filters and the relaxation of the need for polarization insensitive converters, since the input internal wavelength at which one stage, tunable converter of Fig. 1 operates can be at a fixed polarization state and the second converter stage 16, 18, 20, 22 can be fabricated using polarization sensitive waveguide 25 technology.
• Cross phase modulation in an interferometer 12, 14 employing semiconductor optical amplifiers 16, 18 is considered to be the leading method at this time due to the conversion efficiency, extinction ratio enhancement, and low chirp. It is very attractive to incorporate laser 10 providing the continuous wave light on the same chip 26 as the interferometer 12, 14 due to the elimination of two optical fiber pigtails and the similarity in the fabrication processes required to produce both devices.
• DBR laser 10 should be chosen as the continuous wave source due to the inherent isolation properties of the laser mirrors.
• SGDBR sampled-grating-distributed-Bragg-reflector
• the device is comprised of a SGDBR laser 10 coupled to a Mach-Zender interferometer 12, 14 with a polarization insensitive semiconductor optical amplifier 16, 18 located in each the arms 20 and 22 respectively.
• a schematic of the device is shown in Fig. 1.
• BTS 10 is a 2 ⁇ m wide buried ridge stripe (BRS) waveguide device that is
• lasers 10 of this type can be made to tune over more than 40 nm with continuous wavelength coverage.
• the laser waveguide 32 is coupled into a 3 dB multimode interference coupler 34 (chosen for its wavelength insensitive splitting ratio) that forms the input of the Mach-Zender interferometer 12, 14.
• the input signal, ⁇ is coupled from an optical fiber (not shown) to a waveguide 36 on the integrated optic chip 26.
• a spot size converter 126 can be used to enhance the efficiency of this coupling.
• the input signal, ⁇ may be passed through a polarization insensitive semiconductor optical amplifier 38 before being combined in another 3-dB coupler 40 with the continuous wave light from tunable laser 10.
• This front end semiconductor optical amplifier 38 allows wavelength conversion in the second stage to be performed over a larger range of input signal powers, since it can be used as a gain control element.
• This front end semiconductor optical amplifier 38 allows wavelength conversion in the second stage to be performed over a larger range of input signal powers, since it can be used as a gain control element.
• the transverse device structure of optical chip 26 is comprised of a thick low bandgap waveguide layer with multi-quantum well active regions placed above it.
• the thick low bandgap waveguide layer is necessary for good carrier-induced index change in the tuning sections.
• Nonabsorbing passive elements are formed by selectively removing the quantum wells from on top of the waveguide layer.
• the use of the offset quantum wells allows the formation of active and passive sections in a single waveguide layer without having to perform a butt joint regrowth. This, allows the device to be fabricated with only two metal organic chemical vapor deposition (MOCVD) growth steps.
• MOCVD metal organic chemical vapor deposition
• a key advantage of the monolithic wavelength converter is that it can be fabricated using many of the steps already required for tunable lasers 10, making it relatively easy to integrate on chip 26.
• a base structure generally denoted by reference numeral 100
• MOCVD near atmospheric metalorganic chemical vapor deposition
• tertiarybutlyphosphine and tertiarybutylarsine for the group V sources.
• a 0.16 ⁇ m Zn doped InP cap layer 102 is disposed on a strained multiquantum well active region 104.
• Below InGaAsP waveguide 108 is a 0.5 ⁇ m Si doped InP layer 110.
• Two 0.10 ⁇ m InGaAsP waveguides or layers 112 and 114 characterized by an bandgap, Eg 1.127 eV sandwich a 0.5 ⁇ m Si doped InP layer 116.
• Passive sections in the waveguide layer 108 of chip 26 are formed by selectively etching off the cap layer and then quantum well layer 104 as shown in Fig. 4b.
• the sectional view of Fig. 4b is in the direction of light propagation.
• the gratings in laser 10 are formed for the laser mirrors using a dry etch process in region 120 shown in Fig. 4b.
• Region 120 is where active devices will be fabricated while region 122 is where passive devices will be fabricated.
• Regions 120 and 122 are covered by a thick MO VCD regrown layer 124 of InP as shown in Fig. 4c.
• an optical spot size converter 126 at this point into the waveguide layer 108 by performing a diffusion limited etch to taper the thickness of waveguide layer 108 as shown in Fig. 4d before those regions which in which the facets of the laser will be formed.
• the DBR mirrors are then formed by opening a window through cap layer 108 and quantum well layer 104.
• a grating structure 128 is then formed into waveguide layer 108 in chip 26 using selectively reactive ion etching in methane-hydrogen-argon (MHA) as shown in Fig. 4e.
• MHA methane-hydrogen-argon
• a ridge is patterned into structure 100 using reactive ion etching in methane-hydrogen-argon (MHA) into active section 120, grating section 128, passive section 122 or spot size converter 126 as shown in cross sectional transverse side view taken perpendicularly across the direction of light propagation as shown in Figs. 4f(l) - 4f(4) as would be seen through sectional lines 1 - 1 to 4 - 4 of Fig. 4e respectively.
• a wet etch (Br:Methanol) is used to remove the damaged layer from the reactive ion etch (RIE).
• RIE reactive ion etch
• MOCVD step as shown in Fig. 4g, a 3 - 4 ⁇ m p-lnP upper cladding layer 130
• a lOOnm InGaAs contact layer 132 are regrown yielding the structures shown in longitudinal view or in the plane of the direction of light propagation as depicted in Fig. 4g.
• Isolation between the adjacent laser 10 section and between the semiconductor optical amplifier's 16, 18, 38 is achieved by adding a contact layer 133 and etching off the InGaAs layer 132 and performing a deep proton 25 (H + ) implant 134 as shown in Fig. 4h.
• the proton implant is also used to limit the area of the parasitic p-n InP junction 136 shown in Fig. 4i(l) surrounding the buried ridge stripe 138 and to lower the loss in the passive waveguide regions 122 by compensating the Zn acceptor atoms in these areas 140.
• Active section 120, grating section 128, passive section 122 and spot size converter 126 are shown in cross sectional transverse side view taken perpendicularly across the direction of light propagation as shown in Figs.
• the original wavelength will also pass through the comb filter, so an additional filter is needed to block the original wavelength. This limits the flexibility of the tunable wavelength converter 11 as it can now no longer convert to the same wavelength as the input and the filters need to be specified for a given input wavelength.
• Fig. 2 A more flexible implementation is illustrated in Fig. 2 where wavelength conversion is performed in two stages.
• Figs. 2 and 3 show the device as a combination of an integrated device and off-chip components, but 25 the scope of the invention expressly contemplates that all components of Fig. 2 could be integrally fabricated on chip 26 using the above processes.
• Fig. 3 depicts the preferred embodiment of a fully integrated device.
• the first stage converts the signal to an out of band wavelength using distributed feedback (DFB) laser 48 using a cross gain modulation wavelength conversion technique which is then converted to the desired wavelength via cross phase modulation in the tunable wavelength converter 11.
• DFB distributed feedback
• any wavelength channel can be converted to any other wavelength channel without adjusting the filters 42 and 44.
• Conversion to a fixed internal wavelength also allows a choice of only wavelength up- or down-conversion for any input wavelength, ⁇ increment allowing the tunable wavelength converter to be optimized for converting from a specific wavelength instead of having to accept any wavelength.
• Another advantage is the relaxation of the need for polarization insensitivity in the second stage tunable wavelength converter 11 by using a polarization insensitive semiconductor optical amplifier 38 in the first stage and preserving the polarization of the intermediate wavelength when coupling to the second stage. Not having to be polarization insensitive greatly simplifies the active region growth and improves the tunable laser performance.
• Fig. 2 The general approach illustrated in Fig. 2 can also be implemented in a monolithic device by performing the first stage conversion using counter 25 propagating cross gain modulation within an semiconductor optical amplifier 38 integrated on chip 26.
• a diagram illustrating the layout of such an integrated device is shown in Fig. 3.
• the input wavelength travels in the opposite direction to the intermediate wavelength and the output wavelength
• Fig 2 is a block diagram in which non-integrated components are used, namely filters which cannot be easily integrated monolithically.
• Fig. 3 is a monolithic version of an analogous optical circuit to that shown in Fig. 2.
• Fig 3 If one wanted to describe the operation of Fig 3 as a block diagram, it would that shown in Fig 2 except the input signal, ⁇ ,, would be injected after SOA 38, however, and is sent towards SOA 38 (i.e. in the opposite direction of the arrows in Fig. 2). In the integrated case in Fig. 3, 1510nm pass filter 44 is no longer necessary because the input signal does not need to be blocked from reaching the tunable wavelength converter stage 11.

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  • 2000-09-28 AU AU77275/00A patent/AU775671B2/en not_active Ceased
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  • 2000-09-28 WO PCT/US2000/026655 patent/WO2001024329A1/en not_active Application Discontinuation
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